1. Field of the Invention
The present invention relates to a method and apparatus for supplying a predetermined amount of a pelletized metal halide (hereinafter referred to as a xe2x80x9cpelletxe2x80x9d) to a chamber part of an arc tube when producing an arc tube for a discharge lamp having a sealed chamber part with electrodes, a light emitting substance such as mercury, and a metal halide sealed therein.
2. Description of the Related Art
As shown in FIG. 12, according to a conventional apparatus such as disclosed in JP-A-62-118340U, a rotor 1 having recess parts 2 for holding pellets P on its outer periphery and a hopper 3 for storing the pellets P therein such that the outer circumferential surface of the rotor 1 faces the inside of the hopper 3, with a suction space part 5 and an exhaust space part 6 provided in the rotor 1. A hole 7, provided in the recess part 2 of the rotor 1, communicates with the suction space part 5 or the exhaust space part 6 for providing a suction or exhaust path so that the pellets P in the hopper 3 enter into the recess parts 2 so as to be held by adsorption. The pellets P are discharged by the exhaust through hole 7 when the recess parts 2 storing the pellets P reach the scheduled discharging position according to the rotation of the rotor 1.
However, according to the conventional technique, since the hopper 3 is provided outside the rotor 1, the apparatus is bulky. In addition, since the pellets (metal halide) P are highly hygroscopic, they deliquesce when they are exposed to the atmosphere. When this occurs, it is difficult to supply the pellets one at a time to the chamber of the arc tube. In addition, metal halide pellets, such as those used here, that absorb moisture drastically, deteriorate the lamp characteristics.
In view of the problems of the conventional technique, an object of the present invention is to provide an apparatus and method for supplying pellets without the risk of enlarging the apparatus size while preventing moisture absorption of the pellets by disposing a rotation drum provided with a pellet storage room in a sealed case with an inert gas supply.
In order to achieve these objectives, one embodiment of the present invention is an apparatus and method for supplying pellets to an arc tube for a discharge lamp by picking up one pellet from a group of pellets, made from a metal halide. These pellets are stored in a pellet storage room comprising a main body case with a rotation drum storage part opened in the front surface side, a lid to be mounted on the front surface opening part of the apparatus main body case for sealing the rotation drum storage part, a rotation drum disposed rotatably in the rotation drum storage part with the pellet storage room having a rotating member shape formed on the front surface side facing to the lid, and a pellet supply nozzle elongating from the apparatus main body, wherein through holes having a size capable of inserting a pellet are provided on the circumferential wall of the rotation drum with an equal interval in the circumferential direction. In addition, the part of the apparatus main body case facing the circumferential wall of the rotation drum is provided with an arc-like slidably contacting surface to be contacted with the circumferential wall of the rotation drum slidably for holding the pellets stored in the through holes in the through holes, a gas supply hole for supplying an inert gas into the pellet storage room via the through holes, and a pellet discharging hole communicating with the pellet supply nozzle, for discharging the pellets in the through holes at the time it coincides with the pellet storing through holes according to rotation of the rotation drum.
According to rotation of the rotation drum, a pellet enters into the through hole at the substantially lowermost position by its self weight. Since the slidably contacting surface elongates in the circumferential direction below the through holes, even in the case the rotation drum rotates, the pellet in the through hole is supported by the slidably contacting surface from below so as to be held in the through hole. According to rotation of the rotation drum, the through hole with the pellet stored (hereinafter referred to as the xe2x80x9cpellet storing through holexe2x80x9d) moves upward so as to be separated form the pellet group in the pellet storage room. When the pellet storing through hole reaches the position corresponding to the pellet discharging hole, the pellet is discharged into the pellet discharging hole according to the pellet""s own weight and according to the inert gas flow from the inside of the pellet storage room to the pellet discharging hole via the pellet storing through hole. The pellet discharged into the pellet discharging hole is supplied to the chamber part of the arc tube by the pellet supply nozzle. According to further rotation of the rotation drum so that the next pellet storing through hole reaches the position corresponding to the pellet discharging hole, similarly, the pellet is discharged into the pellet discharging hole so as to be supplied to the chamber part of the arc tube by the pellet supply nozzle. Accordingly, the pellets are supplied successively, one at a time.
Since the pellet storage room is provided in the rotation drum disposed in the apparatus main body case (rotation drum storage room) and a large number of pellets can be stored in the pellet storage room, unlike the conventional apparatus, the hopper needs not be provided outside the rotation drum (rotor). Since the inert gas is introduced from the gas supply hole provided in the apparatus main body case and the through holes provided on the circumferential wall of the rotation drum into the pellet storage room so that the inside of the pellet storage room can be maintained in the inert gas atmosphere, the problems of the deliquescence of the pellet in the pellet storage room by the contact with the atmosphere or excessive moisture in the pellets can be prevented.
Another aspect of the present invention is the method and apparatus for supplying pellets to an arc tube for a discharge lamp wherein the rotation drum storage part has an inner circumferential surface formed in a cylindrical shape to be contacted slidably with the circumferential walls entire circumference of the rotation drum as well as the gas supply hole, and is provided with a manifold elongating in the circumferential direction for ensuring communication with at least one of the through holes. Wherever the rotation drum is disposed with respect to the circumferential direction, communication between the gas supply hole and the through holes can be ensured via the manifold so that the inert gas is always introduced into the pellet storage room.
In particular, the inert gas introduced into the pellet storage room via the gas supply hole, the manifold, and the through holes form an inert gas flow from the through hole at a position close to the pellet discharging hole, passing through the gap (slidably contacting surface) between the rotation drum and the rotation drum storage part so as to flow into the pellet discharging hole. The inert gas flow from the inside of the through hole (inside of the pellet storage room) toward the outside (outside of the pellet storage room) promotes storage of the pellet into the through hole by dropping at the scheduled storing position and forces the pellet in the through hole until the pellet storing through hole reaches a position that corresponds to the pellet discharging hole according to rotation of the rotation drum. Since the inert gas in the pellet storage room can easily flow into the pellet discharging hole from the pellet storing through hole when the pellet storing through hole reaches the position corresponding to the pellet discharging hole, the inert gas flow facilitates the discharge of the pellet in the through hole into the pellet discharging hole. Furthermore, in the case the pressure in the pellet storage room is larger than the atmospheric pressure, when the pellet storing through hole reaches the position corresponding to the pellet discharging hole, the pressure in the pellet storage room is released via the pellet discharging hole and the inert gas flows out by the speed according to the pressure and the pellet is discharged at the same time.
Another embodiment of the present apparatus and method for supplying pellets to an arc tube for a discharge lamp has an arc-like slidably contacting surface provided facing the area of the substantially lower half of the circumferential wall of the rotation drum. Wherever the rotation drum is disposed with respect to the circumferential direction, communication between the through holes at a position not facing the arc-like slidably contacting surface and the gas supply hole can be ensured via the gap between the upper half of the circumferential wall and the inner circumferential surface of the rotation drum storage part so that the inert gas is always introduced into the pellet storage room.
Another embodiment of the present apparatus and method for supplying pellets to an arc tube for a discharge lamp according to any of the before mentioned embodiments has a gas pressure in the pellet storage room of the apparatus being maintained in the range from 0.02 to 0.1 kg/cm2 by adjusting the pressure of the inert gas to be supplied to the gas supply hole. It is preferable that the gas pressure in the pellet storage room is higher than the pressure outside the pellet storage room so that the discharge of the pellets, stored in the through holes, is facilitated. However, if the gas pressure in the pellet storage room is too high, there is a risk of storing a plurality of pellets in a through hole at the same time which may cause choking or cracking of the pellets. Therefore, in order to discharge the pellets from the discharging hole smoothly, without choking the through holes or cracking the pellets, it is preferable to set the gas pressure in the pellet storage room at a predetermined value in the range from 0.02 to 0.1 kg/cm2.
Another embodiment of the present apparatus and method for supplying pellets to an arc tube for a discharge lamp according to any of the previous embodiments is an apparatus having a lid, provided so as to be opened or closed by swaying around the part supported by the apparatus main body case. The pellet storage room can be opened by swaying the lid for refilling a new pellet group in to the pellet storage room.
Another embodiment of the present apparatus and method for supplying pellets to an arc tube for a discharge lamp according to any of the previous embodiments is a V-shaped groove provided on the inner circumferential wall of the rotation drum comprising the pellet storage room as well as the through holes provided on the bottom part of the V-shaped groove. Since the pellet group in the pellet storage room gather at the bottom part of the V-shaped groove according to its self weight, even in the case the amount of the pellet group remaining in the pellet storage room is small, the pellets can be introduced into the through holes.
Another embodiment of the present apparatus and method for supplying pellets to an arc tube for a discharge lamp according to any of the previous embodiments is a through hole with a depth H, formed in the range from D/2 less than Hxe2x89xa6D with the proviso that the inner diameter of the through holes is D. In the case the depth H of the through holes is larger than the hole diameter D, entrance of two or more pellets into the discharge holes can be allowed. This may cause choking or supply of two or more pellets to the chamber of the arc tube at the same time. Moreover, in the case the depth H of the through holes is smaller than xc2xd of the hole diameter D, there is a risk of discharge of the pellet from the through hole before the pellet storing through hole reaches a position corresponding to the pellet discharging hole so as to return the pellet to the group of pellets before delivering it to the chamber of the arc tube. Accordingly, the depth H of the through holes is set in the range from D/2 less than Hxe2x89xa6D. D being the inner diameter of the through holes.